Experimental study on roll-bond collector/evaporator with optimized-channel used in direct expansion solar assisted heat pump water heating system

In this investigation, a direct expansion solar assisted heat pump (DX-SAHP) water heating system using an optimized-channel roll-bond collector/evaporator was designed, fabricated and tested. Optimized fractal T-shape and honeycomb shaped channel patterns were adopted to improve the thermal performance of the roll-bond panel, which acts as both the evaporator for the heat pump system and the collector for solar thermal utilization. The performance of the studied water heating system using the south-faced, wall-mounted roll-bond panel with the new composite channel patterns was investigated experimentally. Results show that, under the experimental conditions, the roll-bond panel with optimized channel pattern shows better thermal properties, and the performance the DX-SAHP system is significantly enhanced by using the roll-bond panel with optimized channel pattern. Compared to the conventional parallel channel pattern, fractal T-shaped channel pattern enhanced COP of the system by 14.6%, and heating capacity by 17.3%. And the honeycomb shaped channel pattern further enhanced COP and heating capacity of the system by 5.9% and 6.2%. •Roll-bond panel is used as the collector/evaporator.•Flow channel structure of the roll-bond panel is optimized.•The optimized channel pattern enhances the performance of the roll-bond panel.•The honeycomb shaped channel pattern shows best performance.